Four major groups of Protozoa is as follows:
a. Amoeboid protozoans: The amoeboid protozoans live in freshwater, sea water or in moist soil. They produce pseudopodia for locomotion and for capturing food. The marine forms have silica shells on their surface. Some of them are parasites, e.g. Entamoeba histolytica.
b. Flagellated protozoans: They are either free-living or parasitic. Flagella is present for locomotion. Many of them are parasites, e.g. Trypanosoma.
c. Ciliated protozoans: They are aquatic. Cilia are present for locomotion. A cavity (gullet) is present which opens to the outside of the cell surface. The coordinated movement of cilia facilitates the entry of food-laden water into the gullet. Example: Paramoecium.
d. Sporozoans: The sporozoans have an infectious spore-like stage in their life cycle. Example: Plasmodium.
